1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and an electrophotographic apparatus. The present invention particularly relates to an electrophotographic photosensitive member having an intermediate layer and a surface layer (hereinafter, the intermediate layer including aa-SiC will be also described as “aa-SiC intermediate layer”, and the surface layer including aa-SiC will be also described as “aa-SiC surface layer”) including hydrogenated amorphous silicon carbide (hereinafter, also described as “aa-SiC”), and an electrophotographic apparatus having the electrophotographic photosensitive member.
2. Description of the Related Art
An electrophotographic photosensitive member having a photoconductive layer (photosensitive layer), which includes an amorphous material, on a substrate (conductive substrate) is widely known. In particular, electrophotographic photosensitive members having photoconductive layers of amorphous silicon (hereinafter, also described as “a-Si”) formed on substrates of metals by layer forming techniques such as a chemical vapor deposition method (CVD method) and a physical vapor deposition method (PVD method) have been already commercialized. Hereinafter, a photoconductive layer including a-Si will be also described as an “a-Si photoconductive layer”, and an electrophotographic photosensitive member having the a-Si photoconductive layer will be also described as an “a-Si photosensitive member”. As a basic constitution of such an a-Si photosensitive member, a positively chargeable a-Si photosensitive member 5000 as illustrated in FIG. 5B is known. The positively chargeable a-Si photosensitive member 5000 has a constitution in which a photoreceptive layer 5002 including a-Si is formed on a conductive substrate 5001, and an aa-SiC surface layer 5005 is further formed on the photoreceptive layer 5002.
Further, as shown in FIG. 5A, providing an intermediate layer 5006 between a photoconductive layer 5004 on a charge injection inhibition layer 5003 and the aa-SiC surface layer 5005 is known. Further, it is known that the photosensitive characteristics are improved by controlling the content of the atoms forming the photoconductive layer 5004 or the aa-SiC surface layer 5005 in the region in the vicinity of the interface between the photoconductive layer 5004 and the aa-SiC surface layer 5005. Japanese Patent Application Laid-Open No. H07-175244 discloses the art of producing an a-Si photosensitive member so that the content of hydrogen atoms in the vicinity of the interface between the photoconductive layer and the surface layer is larger than the content of the hydrogen atoms of any one of the photoconductive layer and the surface layer in the a-Si photosensitive member made by forming the a-Si photoconductive layer and the aa-SiC surface layer on the substrate. Like this, by forming the region having a high content of hydrogen atoms in the vicinity of the interface between the photoconductive layer and the surface layer, an a-Si photosensitive member excellent in photosensitivity can be produced.
Further, Japanese Patent Application Laid-Open No. 2002-123020 discloses the art of producing a negatively chargeable electrophotographic photosensitive member having the maximum value in the distribution in a layer thickness direction (stacking direction) of the content percentage of the carbon atoms in the surface layer, in the a-Si photosensitive member made by forming an a-Si photoconductive layer and an aa-SiC surface layer on a substrate. In Japanese Patent Application Laid-Open No. 2002-123020, the electrophotographic photosensitive member excellent in charging performance at the time of negatively charging, sensitivity, optical memory and image deletion can be produced by making the content percentage of carbon atoms nonuniform in the layer thickness direction so as to have a peak region in which the content percentage of carbon atoms in the surface layer is 85 to 95 atomic %. Further, Japanese Patent Application Laid-Open No. 2004-133397 discloses the art of producing an electrophotographic photosensitive member having two or more maximum values in the distribution in the layer thickness direction of the content percentage of the carbon atoms in the surface layer in the a-Si photosensitive member made by forming an a-Si photoconductive layer and an aa-SiC surface layer on a substrate. Japanese Patent Application Laid-Open No. 2004-133397 also discloses the art of producing an electrophotographic photosensitive member in which the content percentage of the elements belonging to the 13th group of the periodic table in the surface layer also has the maximum value in the distribution in the layer thickness direction. In Japanese Patent Application Laid-Open No. 2004-133397, the electrophotographic photosensitive member excellent in photosensitive characteristics with less image defection can be produced by alternately distributing the maximum value of the content percentage of the carbon atoms and the maximum value of the content percentage of the elements belonging to the 13th group of the periodic table in the surface layer in the layer thickness direction.
In recent years, in the market, speedup and colorization of electrophotographic apparatuses have proceeded, and the electrophotographic process is changed to the one that is easily worn as compared with the conventional apparatus. To these market requests, improvement in the electrophotographic apparatuses is necessary, and the electrophotographic photosensitive members are needed, which can realize longer lives while keeping favorable photosensitive characteristics at the same time. In order to increase the life in an electrophotographic photosensitive member, it is necessary to increase the thickness of the aa-SiC surface layer, or enhance the hardness of the aa-SiC surface layer itself while keeping favorable photosensitive characteristics. However, when the surface layer is formed on the photoconductive layer to be thick, if a sudden environmental change (sudden change in temperature and humidity) occurs, separation sometimes occurs in the vicinity of the interface between the photoconductive layer and the aa-SiC surface layer. As one example of the sudden environmental change, transportation of electrophotographic photosensitive members by aircraft is cited.
The separation which occurs in the vicinity of the interface between the photoconductive layer and the aa-SiC surface layer is considered to be caused because the internal stress of the surface layer itself becomes larger as the layer thickness of the a-Sic surface layer is made larger. The reason for this is considered to be that as the thickness of the aa-SiC surface layer becomes larger, the difference in the internal stress between the photoconductive layer and the aa-SiC surface layer becomes larger, and therefore, stress concentrates in the vicinity of the interface between the photoconductive layer and the aa-SiC surface layer. Further, enhancement of the hardness of the aa-SiC surface layer itself can be achieved by adopting an aa-SiC surface layer denser than the conventional one. However, when a dense aa-SiC surface layer is formed on the photoconductive layer, if a sudden environmental change occurs, separation sometimes occurs in the vicinity of the interface between the photoconductive layer and the aa-SiC surface layer, as in the case of increase of the thickness of the aa-SiC surface layer. The cause of separation which occurs in the vicinity of the interface between the photoconductive layer and the aa-SiC surface layer is the same as in the case of increase of the thickness of the aa-SiC surface layer. More specifically, this is considered to be because the internal stress of the aa-SiC surface layer itself becomes larger, as the aa-SiC surface layer is made denser, and therefore, the stress concentrates in the vicinity of the interface between the photoconductive layer and the aa-SiC surface layer.
From the above, it is a difficult problem to keep favorable adhesion of the photoconductive layer and the aa-SiC surface layer when a sudden environmental change occurs, in case that the aa-SiC surface layer with high internal stress is formed on the photoconductive layer in the conventional electrophotographic photosensitive member.